Coating compositions based on polymeric resinous binders are used to coat the surfaces of containers such as food and beverage cans. The resinous binders may be spray applied to the interior surface of the can or applied to a continuous metal strip using a coil coating process and the coated strip formed into a can body or a can end. Consequently, the polymeric resinous binder must possess a variety of properties. It should be safe for food contact; have good adhesion to the substrate; resist degradation and be flexible to tolerate the various fabrication steps. Polymeric binders based on epoxy resins made from bisphenol A have for many years been the polymeric binder of choice because the resultant coating has good overall properties for container applications. Unfortunately, these compounds are perceived as being potentially harmful to human health. Consequently, there is public sentiment to eliminate these polymers from container coatings.
Polyurethanes made from the reaction of polyisocyanates with polyols have been proposed as replacements for bisphenol A-containing polymers. However, polyisocyanates can cause respiratory problems and are difficult to work with. Also, end users of coating compositions made from such polyurethanes are reluctant to use such compositions with food-contacting coatings because of the danger of isocyanates being extracted from the coating. Consequently, it would be desirable to have coating compositions based on a polymer binder that has the good overall properties of polyurethanes but does not have the problems associated with the use of polyisocyanates.